The invention relates to a pressure package system for providing a working pressure on a fluid included in a pressure package, the system being provided with a pressure package in which a product chamber is included for holding the fluid and in which a working pressure chamber is included for keeping a propellant at the working pressure, the system being further provided with a pressure controller and a high-pressure chamber connected with the pressure controller for keeping the propellant in supply at a relatively high pressure, the system being further arranged to supply the propellant from the high-pressure chamber to the working pressure chamber with the aid of the pressure controller on the basis of a reference pressure, for maintaining the working pressure in the working pressure chamber.
Such a pressure package system is known from WO 99/62791. In this known system, the pressure controller with the high-pressure chamber connected thereto, is included in the pressure package as a pressure control device. The pressure package is of elongate and substantially cylindrical design. The pressure control device is so designed as to align with the inner walls of the cylinder jacket. The pressure control device can move in an axial direction of the pressure package under the influence of pressure differences in the pressure package. In this known system, the pressure control device constitutes the separation between the product chamber and the working pressure chamber. It will be clear that a “high-pressure chamber connected with the pressure controller” is understood to mean a high-pressure chamber and a pressure controller between which a fluid communication can be effected for the purpose of controlling the working pressure with the aid of a propellant from the high-pressure chamber.
The reference pressure is slightly lower than a predetermined working pressure which it is desired to apply to the fluid operatively included in the product chamber. The working pressure is a pressure to be kept substantially constant. The known system works as follows. When the pressure in the product chamber starts to decrease to a new pressure in the product chamber because, for instance, a user has allowed fluid to flow from the pressure package, the pressure control device moves, as a result of the pressure difference between the working pressure chamber and the product chamber, in the direction of the product chamber. The volume of the working pressure chamber thereby increases and, as a result, the pressure in the working pressure chamber decreases. In that case, the reference pressure is higher than the new pressure in the working pressure chamber. The pressure control device is arranged in that case to allow propellant to flow from the high-pressure chamber to the working pressure chamber. As a result, the pressure in the working pressure chamber increases until in the working pressure chamber the pressure has become slightly higher than the reference pressure. The working pressure is then higher than the pressure in the product chamber again, and under the influence of the pressure difference between the product chamber and the working pressure chamber the pressure control device moves a little further in the direction of the product chamber. Since the volume of the product chamber thereby decreases slightly, the pressure in the product chamber will increase slightly. With the decrease of the volume of the product chamber, the volume of the working pressure chamber increases again. The pressure in the working pressure chamber is then a bit lower again than the reference pressure, and the pressure control device will again allow a bit of propellant to flow to the working pressure chamber, etc.
When the pressure prevailing in the working pressure chamber is slightly higher than the reference pressure, the supply of propellant from the high-pressure chamber to the working pressure chamber will block. The pressure control device will then assume such a position that the pressure in the working pressure chamber and the pressure in the product chamber are equal to each other. In that case, this pressure will be the intended working pressure which is slightly higher than the reference pressure.
In the known system, for separating the working pressure chamber and the product chamber, the pressure control device is provided with sealings which abut the inner wall of the cylindrically designed pressure package in such in way as to provide a gas-tight closure between the working pressure chamber and the product chamber. Further, the sealings abut the inner wall in such a way that the pressure control device is still movable in the axial direction of the pressure package under the influence of a pressure difference between the working pressure chamber and the product chamber. As a consequence, in order for the pressure control device to move, much friction is to be overcome. As a consequence of this, in turn, the pressure difference between the working pressure chamber and the product chamber must be relatively great before this difference is annulled.